Cellular plastic polyurethane foams are conventionally made by mixing ingredients and curing the polymerizing mass in a mold. Thus, U.S. Pat. No. 2,814,600 describes mixing polythiourethane with water and a tertiary amine catalyst. The reaction of the polymer with water releases carbon dioxide, with the result that the mass foams into a cellular material.
Various other materials have been combined with di-isocyanate or di-isocyanate-type materials in an attempt to improve the resulting molded cellular molded plastics. For example, certain polyesters were introduced in U.S. Pat. No. 2,779,689; certain polyamines and polyaclcohols in U.S. Pat. No. 2,850,464; certain polymeric materials with an active hydrogen in U.S. Pat. No. 2,888,413; and certain polyhydric, polyalkylene ethers in U.S. Pat. Nos. 3,055,845; 3,252,943; and 4,454,251. In these disclosures, the cellular foam is made as stated by mixing the components and then subjecting the mixture to heat until the material has cured. This batch wise method restricts production of the foams and requires substantial amounts of energy consumption.
Conventional spraying of cellular plastic materials offers a quicker, more convenient process of production. Polyurethane foams have been conventionally by spraying a monomer (or prepolymer) onto a substrate. The polymerizing agent is combined with the monomer to form the cellular plastic either in a simultaneous spraying of the prepolymer and polymerizing agent or by subsequently spraying the polymerizing agent onto the same substrate.
As with the mold-cured plastics above, addition of various organic compounds has been made in an effort to improve the result of the foam. Among the materials that have been added are certain polyesters, in U.S. Pat. No. 2,779,689; and certain polyether polyols, in U.S. Pat. Nos. 4,543,366; 4,649,162; and 4,950,695.
Despite these efforts, several problems still occur in industrially produced polyurethane foams. First, these foams usually contain chlorofluorocarbon compounds as "foaming agents". That is, as an agent which generates gas in the mixture of monomer and catalyst to impart cellular structure. However, in recent years, these chlorofluorocarbon compounds have been criticized as contributing to the depletion of ozone in the atmosphere. As a result, the use of chlorofluorocarbons is being restricted by Legislation and regulation in many countries.
Another problem with industrially produced conventional foams is poor density and low compressive strength. Industrial produced foams should have relatively light density, yet be sufficiently strong to support weights and withstand foreseeable impact. Those conventional foams which have been sufficient compressive strength have generally had too great a density to be desirable. Further problems in conventional foams include high density of the materials to be sprayed. Excessive viscosity of sprayable materials results in frequent clogging of the spraying mechanisms, leading to production interruption with inefficiency. Another problem of conventional foams is surface friability, which not only makes the finally produced foam unattractive but renders it vulnerable to wear over time. Conventional materials which are sprayed to form foams often have sensitivity to ambient humidity, requiring that they only be sprayed on days with low atmospheric humidity. When such materials are sprayed on damp days or in damp conditions, the resultant foam is weakened. One final problem which affects conventional foams is reactivity to substrate temperatures. When foams are sprayed onto substrates which undergo great variations in temperature, many conventional foams suffer structural damage due to insensitivity.